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FreeBSD-EN-18:12.mem                                            Errata Notice
                                                          The FreeBSD Project

Topic:          Small kernel memory disclosures in two system calls          

Category:       core
Module:         kernel
Announced:      2018-09-27
Credits:        Thomas Barabosch, Fraunhofer FKIE
Affects:        All supported versions of FreeBSD.
Corrected:      2018-09-27 18:42:40 UTC (stable/11, 11.2-STABLE)
                2018-09-27 18:36:30 UTC (releng/11.2, 11.2-RELEASE-p4)
                2018-09-27 18:36:30 UTC (releng/11.1, 11.1-RELEASE-p15)
                2018-09-27 18:44:40 UTC (stable/10, 10.4-STABLE)
                2018-09-27 18:36:30 UTC (releng/10.4, 10.4-RELEASE-p13)
CVE Name:	CVE-2018-17155

For general information regarding FreeBSD Errata Notices and Security
Advisories, including descriptions of the fields above, security
branches, and the following sections, please visit
<URL:https://security.FreeBSD.org/>.

I.   Background

The kernel provides an interface for userland programs via system calls. Two
of these system calls are named getcontext and swapcontext.

II.  Problem Description

Due to insufficient initialization of memory copied to userland in the
getcontext and swapcontext system calls, small amounts of kernel memory may
be disclosed to userland processes.

III. Impact

An unprivileged local user may be able to create a specific program to read
the contents of small portions of kernel memory.

Such memory might contain sensitive information, such as portions of the file
cache or terminal buffers.  This information might be directly useful, or it
might be leveraged to obtain elevated privileges in some way; for example,
a terminal buffer might include a user-entered password.

IV.  Workaround

No workaround is available.

V.   Solution

Perform one of the following:

1) Upgrade your system to a supported FreeBSD stable or release / security
branch (releng) dated after the correction date.

Afterward, reboot the system.

2) To update your system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

Afterward, reboot the system.

3) To update your system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch https://security.FreeBSD.org/patches/EN-18:12/mem.patch
# fetch https://security.FreeBSD.org/patches/EN-18:12/mem.patch.asc
# gpg --verify mem.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/10/                                                        r339984
releng/10.4/                                                      r338981
stable/11/                                                        r339983
releng/11.1/                                                      r338981
releng/11.2/                                                      r338981
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-17155>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-18:12.mem.asc>
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